The present invention relates to an air-permeable filter for ink cartridge and an ink cartridge comprising such an air-permeable filter. More particularly, the present invention relates to an ink cartridge comprising an air vent communicating between an inner space for receiving and storing an ink and the outer space and an air-permeable filter to be provided in the air vent.
Most of image forming apparatus such as printer have heretofore employed a mechanism for supplying an ink into a printing head from an ink cartridge. In this mechanism, an ink cartridge which has previously received an ink therein is mounted on a printer or the like in position. Under these conditions, the ink is supplied into the printing head from the ink cartridge. Between the ink cartridge and the printing head may be provided an ink reservoir cartridge for temporarily receiving an ink. As a dispersant for ink component there is normally used water or a mixture of water and an organic solvent having a good compatibility with water (e.g., lower alcohol such as methanol, ethanol, isopropyl alcohol and n-propanol).
However, when the liquid level of the ink descends as the amount of the ink decreases, a negative pressure is produced in the interior of the ink cartridge or the ink passage. When the negative pressure increases, normal ejection of ink is prevented, giving blurred prints. In order to prevent this defect, an air vent is provided in the ink cartridge or ink passage. The air vent is disposed in such a position that it is not dipped in the ink during normal use with the ink cartridge being mounted on the printer. However, when the printer or ink cartridge is tilted during transportation or storage, the air vent can be dipped in the ink, possibly causing the ink to be leaked through the air vent. In order to prevent this defect, it is proposed that an air-permeable filter which is permeable to air but impermeable to liquid, e.g., porous polytetrafluoroethylene (hereinafter referred to as xe2x80x9cPTFExe2x80x9d) be attached to the air vent.
Further, it is a recent tendency that the interior of the ink cartridge or ink passage is pressurized to accelerate the ejection of the ink in order to raise the printing speed of the printer. Moreover, since the ink in the ink cartridge or ink passage can be leaked from the printing head as the ambient temperature of the printer increases, it has been practiced to reduce the pressure in the ink cartridge or ink passage at the end of printing, causing the ink to be sucked up.
Thus, a positive or negative pressure can be applied to the interior of the ink cartridge or ink passage through the air vent. Accordingly, the air-permeable filter has been required to prevent ink leakage steadily.
To this end, an object of the present invention is to provide an air-permeable filter for ink cartridge which can fairly prevent ink leakage. Another object of the present invention is to provide an ink cartridge comprising this air-permeable filter.
The foregoing object of the invention is accomplished with an air-permeable filter for ink cartridge according to the invention which comprises a laminate comprising at least one porous material layer comprising at least one resin selected from the group consisting of fluororesin and polyolefin resin and at least one air-permeable substrate layer having a tensile strength of 1 MPa or more.